Problem: What is the height of Jack's house, in feet, if the house casts a shadow 56 feet long at the same time a 21-foot tree casts a shadow that is 24 feet long? Express your answer to the nearest whole number.
Answer: The ratio of shadow lengths is $\frac{56}{24}=\frac{7}{3}$.

This is the same as the ratio of actual heights, so if $h$ is the height of the house,

$$\frac{h}{21}=\frac{7}{3}\Rightarrow h=\boxed{49}$$